The processing of crystalline structures, in particular glass plates, in ultra-clean rooms was initially necessary in the technique for producing semiconductors. Over time, photovoltaics and the production of TFT screens, inter alia, have proved to be important fields of application for this production technique.
Tailored solar modules make accurate integration into building grids and profiles possible. Semitransparent solar cells, but also opaque solar cells with transparent areas, make photovoltaic glazings appear to be flooded with light. Here, the solar cells often take on the desired effect of protection against the sun and glare.
The production of such photovoltaic systems requires operating conditions such as those which are conventional primarily in the production of integrated electronic circuits. However, in the production of photovoltaic systems, these so-called clean room conditions additionally make it necessary to handle shock-sensitive glass plates with a large surface area.
The production and further processing of shock-sensitive plates is also required in the production of large flat screens, and in a large quantity. Modern flat screens are increasingly replacing the old tube monitors, and are also becoming less and less expensive.
These are based on TFT/LCD technology. In this context, LCD (Liquid Crystal Display) represents the use of liquid crystals in the individual pixels of the screen, and TFT stands for Thin Film Transistor. The TFTs are very small transistor elements which control the orientation, and therefore the light transmission, of the liquid crystals.
A flat-screen display consists of numerous pixels. In turn, each pixel consists of 3 LCD cells (subpixels), corresponding to the colors of red, green and blue. A 15-inch screen (measured diagonally) contains about 800,000 pixels or roughly 2.4 million LCD cells.
For understanding of the mode of operation:
A liquid crystal cell (LCD cell) works in a similar manner to polaroid sunglasses. If two polaroid glasses are held one above the other and then twisted with respect to each other, it is initially possible to see less and less and then nothing at all. This effect arises because polaroid glass is transparent only to light waves which vibrate in a specific plane. If two such glasses are held one above the other and twisted through 90° with respect to each other, some of the light can still pass through the first glass, but no longer through the second glass, since this is then transverse to the incoming light waves and filters them out.
An LCD cell works on the same principle. It consists of two polaroid glasses which are twisted through 90° with respect to each other and through which no light can therefore pass, in accordance with that explained above. A layer of liquid crystals, which has the natural property of turning the vibration plane of light, is located between these two polaroid glasses. This layer of liquid crystals is just thick enough that the light passing through the first polaroid glass is turned back through 90°, and can therefore also pass through the second polaroid glass, i.e. is visible to the viewer.
If the liquid crystal molecules are then turned away from their natural position by the application of an electrical voltage, less light passes through the cell and the corresponding pixel becomes dark. The corresponding voltage is produced by a TFT element which is part of every LCD cell. The light for the LCD display is produced in the rear part of the screen housing by small fluorescent tubes, as are used on a larger scale for illuminating rooms.
Since each pixel has three color filters for the colors of red, green and blue, the control of the transparency of these filters means that each pixel can assume a desired color mixture or a desired color.
For standard office applications, flat screens have outstanding sharpness and a sufficient color quality. In ergonomic terms, TFTs also have much to offer: smaller space requirement, a power consumption which is only a third of that of a tube monitor and significantly lower emission of radiation.
As is conventional in microelectronics, the production of TFT screens requires so-called ultra-clean rooms. This is necessary because, in view of the small size of the line-carrying structures, even small particles can cause line interruptions during the production process. In the production of a TFT screen, such a line interruption would result in the failure of a pixel.
A clean room, or an ultra-clean room, is a room in which the concentration of airborne particles is controlled. It is constructed and used in such a manner that the number of particles introduced into the room or produced and deposited in the room is as small as possible, and other parameters, such as temperature, humidity or air pressure, are controlled as required.
On the one hand, TFT screens are currently becoming less and less expensive, and on the other hand the demand for screens with enormous proportions is increasingly standing out, all the more so because screens of this type firstly can be used very easily at major events and secondly are available in affordable price ranges due to modern production technology.
However, the production of large screens requires the use of special machines even in ultra-clean rooms to handle the large-surface-area, thin glass plates required in this case.
For this purpose, it is possible to use primarily multi-axle industrial robots.
The use of a wide variety of embodiments of multi-axle industrial robots in technology for producing a wide variety of products can be gathered from the prior art. Industrial robots of this type are used in large halls mostly for transporting unmanageable and heavy loads, but can also be used beneficially in the production of smaller machine parts. What matters in all cases is the reproducible precision of the movement sequences of the individual grasping operations, transport movements and setting-down operations.
Here, the conditions in which these movement sequences take place are unimportant in many cases. For example, it is mostly immaterial which noise emission such a movement sequence causes, or whether such an operation is associated with the movement of dust or a more or less large escape of lubricant. Unavoidable abrasion of moving machine parts which cause friction is also mostly unremarkable.
By contrast, natural ramifications of this type must be taken into consideration when working in an environment at risk from contamination, for example in the food-processing industry, in the pharmaceutical industry or even in the production of semiconductors in ultra-clean rooms.
Thus, EP 1 541 296 A1 discloses a manipulator, such as an industrial robot, for use in an environment at risk from contamination, having a number of scavenging chambers, which can be charged with a scavenging medium, in the region of drive units of the manipulator. The object to be achieved in the case of such a device is to further develop the device to such an extent that the manipulator can safely be used in an environment at risk from contamination in a structurally simple manner and therefore, in particular, at low cost.
This object is achieved by a dedicated scavenging chamber being associated with each of a plurality of groups of drive units (claim 1).
Although the environment in which such an industrial robot is to be used is more sensitive to contamination and therefore also places higher demands on the design configuration compared to a normal environment, special demands of this type cannot be compared with the conditions demanded in ultra-clean rooms.
DE 20 2007 003 907 U1 discloses an apparatus for automatically sorting glass plates. This document describes, inter alia, an orienting apparatus (1) which orients the glass plates with respect to a left-hand and/or a right-hand abutment strip (7) via controllable rollers (8), wherein the orienting apparatus (1) comprises two frame roller carriers (10) which can each be rotated separately about a pivot bearing (5). Apart from the fact that this orienting apparatus (1) is not intended for operation in ultra-clean room conditions, in this case the orientation of thick and relatively stable glass plates takes place via impetuous abutments on two abutment strips (7). This is a completely unsuitable orientation process for the orientation of thin glass plates at risk from breaking. This document provides no indication of the particularly smooth, sliding orientation of thin, shock-sensitive glass plates according to the invention.
In the apparatus for transferring and stacking plates described in DE 19 18 791 A, the transfer speed and the stacking speed of plates should be increased considerably compared to a stacking operation according to the prior art, which is partially assisted manually. This is achieved substantially in that the lifting or inverting of each plate is performed in two steps. In order to make it possible to handle the respective plate in the process described here, said plate is connected fixedly by means of a suction device (4), fed to different rotatable carrying devices and moved into different horizontal and inclined positions until it is finally transferred to a stacking portion (11). This document provides no indication of the smooth and soft orientation of thin, shock-sensitive glass plates in ultra-clean room conditions.
DE 10 2005 039 453 A1 further discloses a modular processing system for flat substrates. In order to be protected from dirt, flat substrates of this type, for example TFT screens, are reliant upon enclosures for handling in special atmospheric conditions. According to the invention proposed in this document, an enclosure of the processing system is dispensed with; for this reason, however, the modular processing system is provided with a transfer system which makes both quick access to the individual modules and quick transfer between the individual modules possible, and which makes it possible for the substrates to be transferred between the modules even under ultra-clean room conditions. This is achieved in that the transfer unit has a transfer chamber which accommodates the substrate rest and is in the form of an enclosure, such that the size of the enclosure can be reduced to the size of the substrate, and thus to the imperative size. Although these are measures for optimizing a processing system in a certain way in ultra-clean room conditions, this document does not deal with the topic of orienting thin, shock-sensitive glass plates.
Apart from what has been mentioned above, large, thin glass plates such as those used for producing large TFT screens are extremely sensitive to very small shocks owing to their structure and concurrent relatively large mass. Therefore, an industrial robot is also unsuitable for handling large, thin glass plates in ultra-clean rooms because it lacks sensitivity and in some cases may lack positional accuracy.
In ultra-clean room conditions, the transfer of large, shock-sensitive glass plates from the horizontal orientation to a vertical orientation requires particular care and attention.
A further aspect to bear in mind when maintaining ultra-clean room conditions, particularly when producing expensive products, is the risk of contamination by people. Here, unintended sneezing can destroy a whole production unit. Likewise, such a system requires increased reliability. Since the costs for purchasing and operating an appropriately configured industrial robot are high, a favorable price of such a system is also important.
Particularly when handling large-surface-area glass plates using an industrial robot, it may be observed that large surfaces such as these tend to vibrate as a result of the movement. This can firstly be caused by the suction elements adhering only at a few points and secondly by the accelerated movement sequences of such robots. Vibration phenomena such as these bring the additional risk of glass breakage.